A company is worth what anyone is prepared to pay for it so theres no correct price and three things effect what anyones going to pay for it:
1) Return on investment (ie, profit) - Mr Buyer wants his money back! Its also worth noting that the buyer is only going to get their return from future profits not historic profits. So future projections will be a major factor in a buyers valuation.
2) Commercial risk (or perceived risk, in fact). High risk = low price and low risk = high price. If, for example, a company is reliant on the owner or has one big client, etc..., then clearly this will increase the risk to the buyer thus reducing value. Net assets also effect valuation because if a company has a high net worth (property, stock, IPR, etc,..) this may reduce the commercial risk to the buyer (ie, if the whole things goes belly-up theyre at least left with some assets.)
3) Bidder competition. If you can locate several buyers and get them bidding against each other then youll sell for a great deal more than having just one tyre kicker - market forces will always dictate any companys true value.
Of the above issues, two of them (points 2 & 3) are highly subjective. The third (point 1, profit) is totally objective as far as historic results go but quite subjective in terms of future projections. So two and a half out of three factors are subjective. Regarding the (now one sixth) objective issue of historic profits, an accountant will look at the "adjusted" (real) EBITDA (profit) of a company and apply a multiple (5 is often quoted). However, after all that, it's worth what anyone's prepared to pay for it.